1. Field of the Invention
This invention relates to a system for use with a conventional internal combustion engine, such as an automobile engine, to permit alternative utilization of a liquified gas fuel such as liquified petroleum gas, natural gas, hydrogen or propane and a liquid fuel such as gasoline, alternatively selectable by a manually operated control.
2. Description of the Prior Art
Duel fuel systems having manually actuated selection means are well known in the prior art. Illustrative of early duel fuel systems are the following U.S. Pat. Nos.
______________________________________ Number Issued Inventor ______________________________________ 1,931,698 October 24, 1933 Holzapfel 1,970,425 August 14, 1934 Grabbe ______________________________________
Such systems for use with a liquid fuel and a liquified gas fuel typically consist of three principal elements: (a) a means for selecting the fuel to be utilized, (b) a liquified-to-gaseous fuel converter or vaporizer and (c) a gaseous fuel and air mixer or carburetor. Each of these principal elements will be addressed seriatim.
a. Fuel Selection Means
Most conventional modern propane carburetion equipment utilizes electrically operated solenoid valves for alternative selection of fuels. One valve is normally in the liquid propane line running from the propane storage tank of the vehicle adjacent to the inlet to the propane converter or vaporizer, and another is in the gasoline line supplying the carburetor. Such solenoid valves are typically activated by a single pole double throw switch mounted where it may be conveniently operated by the driver to permit alternative selection of propane or gasoline. Such electrically operated solenoid valves are typically the weakest link in conventional dual fuel carburetion systems. They frequently do not work well in the environment of the engine, and it is difficult to locate a reliable voltage source in the vehicle's electrical system which is the right voltage, is available during engine starting and does not affect the ignition system.
At least one prior art dual fuel system utilizes a vacuum operated solenoid valve in the propane portion of the system but retains an electrically operated solenoid valve in the gasoline portion of the system.
b. Converters
Liquified petroleum gas, propane and the other "gaseous" fuels with which the present invention is intended to be used are normally held for use in a reservoir or tank under sufficient pressure and at a temperature such that the fuels are in a liquid state. Thus, such fuels are referred to as "liquified gas" fuels. Conversion of such liquified fuel to a gaseous state at a pressure and temperature usable by conventional internal combustion engines must be accomplished in a converter structure which is accordingly denominated a "liquified gas to gaseous fuel converter" or a "liquified-to-gaseous fuel converter."
Most conventional liquified gas to gaseous fuel converters are of the two stage variety comprising a relatively small diameter first stage, or primary, diaphragm within a chamber warmed by hot engine coolant liquid, which primary diaphragm controls a normally open inlet valve, and a large diameter second diaphragm which controls a normally closed valve.
U.S. Pat. No. 3,528,787, for "Fuel Carburation Apparatus," assigned to the same assignee as the instant application, disclosed a liquified-to-gaseous fuel converter structure comprising a single diaphragm responsive to engine venturi vacuum which actuates an inlet valve. The present invention improves upon the converter element of that patent and conventional converter structures.
c. Mixers
Early propane mixers consisted simply of a tube affixed in the existing gasoline carburetor at a point where the venturi narrows. These so called "spud ins" were acceptable during a period when gasoline and propane were very inexpensive. Subsequent development was directed toward design of a separate propane venturi, and designs for a separate venturi and separate idling system were developed. However, as one skilled in the art will appreciate, a venturi is not very effective as a metering device when air flow is low and slow. Furthermore, a venturi typically has a narrow control range such that it is difficult to design a venturi which will satisfy both low speed and high speed conditions. Accordingly, an ideal system would incorporate a separately engineered venturi for each speed of air flow.
Several mixer designs have been directed to a variable venturi which used a tapered plug device in the opening of the carburetor, with the plug moving up and down in response to variations in air flow. Inherent limitations in such "variable venturi" or "air valve" carburetors are present due to the weight of the plug and short distance of travel. Typically all engine operation conditions must be accommodated within approximately five-eighths of an inch (15.9 millimeters) of plug travel Additionally, such designs exhibit hysteresis problems and relatively poor fuel economy characteristics. Thus, such problems weigh against the utilization of the variable venturi
The mixer structures disclosed in U.S. Pat. No. 3,528,787 and utilized in similar "SU" type carburetors employ a plunger structure comprising a round piston acted on by venturi vacuum and atmospheric pressure and a smaller round piston or plunger which variably obstructs air flow through an air passage and from which extends a needle positionable in a fuel orifice on the side of the air passage opposite the plunger structure. Such projection of the needle from the plunger results in a relative large mixer structure.
Another prior art mixer utilizes a relatively large diaphragm to regulate air flow and to move a valve needle to cooperate with an orifice in a mixer structure somewhat similar to one embodiment of the mixer of the present invention.
It is therefore an object of the present invention to overcome the problems associated with prior art dual fuel systems.
It is yet another object of the present invention to provide a dual fuel system adaptable for use with original equipment or for addition to existing equipment, which system fills a need for alternatively selectable fuel provision means.
It is a further object of the present invention to provide a dual fuel system having a mixer which can accommodate relatively large variations in the manufacturing tolerances of its parts.
It is a further object of the present invention to provide a duel fuel system which assists in compliance with strict emission control standards for internal combustion engines by providing for utilization of inherently clean burning propane in conventional vehicles.
It is a further object of the present invention to provide a duel fuel system having a gaseous fuel mixer and to provide a mixer having positive fuel control while minimizing hysteresis.
It is a further object of the present invention to provide a duel fuel system having a liquified gas to gaseous fuel converter in which the converter has a valving structure on which undue pressure is not exerted by the valve actuator when the valve is in the closed position.
It is a further object of the present invention to provide a duel fuel system having a liquified gas to gaseous fuel converter with the converter adapted to operate at very low manifold vacuum pressures such as those experienced during engine starting in cold climates.
It is a further object of the present invention to provide a duel fuel system having a liquified gas to gaseous fuel converter which automatically self adjusts to provide an "economy" fuel mixture during cruise conditions.
It is a further object of the present invention to provide a duel fuel system having a liquified gas to gaseous fuel converter which has an inlet valve which positively locks off incoming fuel even if the inlet valve actuator diaphragm breaks
It is a further object of the present invention to provide, in a dual fuel system, a positive acting means for selecting fuel which functions without the use of electricity.
It is a further object of the present invention to provide a duel fuel system having a gaseous fuel and air mixer which is easily adaptable to use with a variety of fuels, including liquified petroleum gas, propane, natural gas and hydrogen as well as other gases usable for combustion in internal combustion engines.
It is a further object of the present invention to provide a dual fuel system utilizing a mixer which is sufficiently compact to occupy substantially only the space within the air cleaner element on conventional engines.